This invention relates to a method for improving material properties of powdered metal parts and, in particular, for producing improvements only at selected surfaces of the parts.
It is well known in the use of powdered metal parts that certain local regions experience stress concentration due to loading and geometry of the parts. It is also generally known that adverse frictional consequences are produced by the sliding wear of parts, or by rolling, or by touching of parts. Stresses are higher at points of applied loads and adversely affect frictional wear characteristics of the parts, in particular, at these localized areas. In addition, localized areas may also be weakened due to manufacturing processes which produce powdered metal parts. In order to improve the material properties between these parts as a result of the causes mentioned, it is customary in the art to heat the entire powdered metal part and to melt metallic material over the entire part thereby producing infiltration of the metallic material within the structure of the part.
This complete envelopment of the powdered metal parts with the metallic material is not only expensive in relation to the amount of metallic material which must be dispensed during this procedure, but also, most of the metal parts are affected by infiltrated material which serve no purpose to the parts. In other words, where it is desired to improve material properties of powdered metal parts in certain local areas only, the entire part is generally affected by the process to improve only a very small localized region thereon.
The present invention has been devised in order to overcome the disadvantages mentioned above by producing local infiltration of infiltrant material directly on the area of the powdered material part which is to be improved. This allows the improvement to effect critical areas without the added expense of the infiltrant required to permeate the entire powdered metal part.
Therefore, it is the principal object of the present invention to produce infiltration of infiltrant material directly on the area which is to be improved.
Another object of the invention is to improve material properties at localized areas due to stress concentrations produced by loading applied to those areas.
Another object of the invention is to improve the material properties of powdered metal parts by a method which is not only economical but also requires a minimum of parts and expenditure of effort.
In order to overcome the difficulties mentioned above and to achieve the objects, the present invention was devised whereby the infiltrant material in the form of a metallic substance is applied solely to the area on the powdered metal which is to be improved by infiltration. While the infiltrant is adjacent the area to be infiltrated, heat in concentrated form, is applied to the infiltrant material and only to this target area. This concentrated heat will produce melting of the infiltrant material for effecting infiltration into the powdered metal part. Since only a local area of the powdered metal part is heated, infiltration will be limited solely to that locally heated area. The concentrated form of heat may be provided by a laser system comprising a device for producing a laser beam arranged for sweeping a light ray repeatedly across the infiltrant material. A controller may be utilized to control the amplitude and period of sweeping the beam, the time in which the beam is to be effective against the material and the amount of power for controlling the temperature. In this manner, the volume of infiltration is accurately controlled to the amount necessary to effect the improvement desired in the material property. In another embodiment, an induction coil is utilized for providing heat in concentrated form upon the infiltrant material. A controller is operatively associated with the coil for varying the current and therefore the temperature produced by the coil, and the time of current application, thereby controlling the extent of the depth of infiltration.